The footer module spans across the site.
The footer is the ideal place to add address information and other types of general information that should be visible on all the pages of your site. The footer module (for D4 skins only) contains 3 columns for rich content and some additional fields for social icons and a branded footer text.
1) Column fields 1-3 are used for content. Using the global data tags (See section 03.07) is recommended as it ensures that your information is always automatically updated in the footer when you make central changes to your data.
2) With the "Social icons"-fields you can link to your Facebook, LinkedIn or other social service. The social icons will show on the page if you enter data and not show if the field is left empty.
3) Bottom text: This field can be used for branding like "This site is powered by…" etc. Can be left empty. This is the default footer for D3 or earlier skins.